All forms of money that circulate in the United States today are forms of credit that also serve as media of exchange. For example, currency is a credit instrument because it is a liability of its issuer, the federal government. Technically, currency is simply a small denomination, non-interest-bearing bearer bond of no fixed maturity that governments issue for just one reason--it provides interest-free debt financing. As a credit instrument, currency serves as a store of value for its owner; as a medium of exchange, it facilitates transactions. Specie, that is, gold and silver coins, is the only form of money that is not credit, but such coins no longer circulate in the economy.

The quote "Technically, currency is simply a small denomination, non-interest-bearing bearer bond of no fixed maturity" just melted my brain today.